Method of conducting string shot operations in an oil well

ABSTRACT

String shot apparatus and method of servicing perforated well casing using one or more explosive cords supported along a wire line and equipped with discriminator means for detonating the cords independently or in groups at the operator&#39;&#39;s option. The wire line includes centralizers designed to be quickly assembled to and detached from the line as well as means for securing the explosive cord to the line in a desired degree of tautness. The explosive cord includes means for eliminating stretch and preferably embodied therein to safeguard against its elongation, ballooning, and looping by frictional or other forces and temperature rise encountered during the servicing operation. A readily opened and closed blowout protector is securable across the well head to seal the well closed about the wire line to avoid a blowout if the servicing operation releases highsubsurface pressures into the well.

United States Patent Grayson Mar. 14, 1972 [54] METHOD OF CONDUCTINGSTRING 3,010,396 11/1961 Coleman ..175/4.55 SHOT OPERATIONS IN AN OILWELL 3,033,114 5/1962 Gieske et al. ..l02/2l.8 3,134,437 5 4 v [721lnvenm" Bobby m? 7306 Pembroke 3,208,378 9x325 1 Avenue, Oildale, Calif.93308 [22] Filed: Oct 28, 1970 Primary Examiner-Verlin R. Pcndegrass[21] Appl No I 84 739 Attorney-Sellers and Brace 57 l Related U.S.Application Data ABSTR C1 String shot apparatus and method otserviciugperforated well DlvlSlOn Of 5611 27,214, P 1970, at casing using one ormore explosive cords supported along a ,245. wire line and equipped withdiscriminator means for detouab ing the cords independently or in groupsat the operator's op [52] U.S. Cl ..l02/21, 166/63, 102/2 1 .8 tion. Thewire line includes centralizeis designed to be quickly [51] Int. Cl..F42d 3/00 assembled to and detached from the line as well as means for[58] Field of Search .,..l02/20, 21, 21,6, 21,8; securing the explosivecord to the line in a desired degree of 166/63, 299; 175/455 tautness.The explosive cord includes means for eliminating stretch and preferablyembodied therein to safeguard against 5 References Cited its elongation,ballooning, and looping by frictional or other forces and temperaturerise encountered during the servicing UNITED STATES PATENTS operation. Areadily opened and closed blowout protector is securable across the wellhead to seal the well closed about the 2,414,349 Alexander l wire lineto avoid a blowout th Servicing operation releasas 2,790,388 4/1957MacLeod ..102/21 6 high subsurface pressures into the we". 2,867,1701/1959 Ktbby ..102/21.8 2,912,932 11/1959 Ayers ..l02/2l 56 Q 50 25Claims, 13 Drawing Figures Patented March 14, 1972 3 Sheets-Sheet 5INVENTOR away 14 654 ysa/v METHOD OF CONDUCTING STRING SHOT OPERATIONSIN AN OlL WELL This application is a division of my application forUnited States Letters Patent Serial No. 27,214, filed Apr. 10, 1970, andnow US. Pat. No. 3,572,245.

This invention relates to string shot apparatus and more particularly toan improved method for performing a cleaning and reconditioningoperation in a well using one or more explosive cords and includingmeans for activating one or a series of string shot operations carriedout at any desired time intervals during a single wire line run-in"operation.

The string shot technique employed to perform servicing operations inoil wells and to improve the flow by clearing away material tending toclog the flow perforations is subject to many shortcomings anddisadvantages avoided by the present invention. This technique utilizesan explosive cord supported along the side of a wire line and lowered toposition the cord opposite a section of perforated casing to be clearedof debris. It is not possible to determine the cause or seriousness ofthe clogged condition and more particularly how strong an explosivecharge is required to clear the perforations yet avoid risk of damage tothe casing. It is costly and timeconsuming to carry out a string shotoperation and this encourages the operators to use an excessivelypowerful charge to avoid having to perform several run-in operations.Not infrequently, the extra strong charge seriously damages the casmg.

Attempts to use explosive cords of low power or strength are uncertainand often result in failure or produce serious damage to the casing orparting of the wire line and loss of the weight required to pull theline into the well for quite different reasons. For example, in certaininstances the cords malfunction or fail to explode or explode over onlya small portion of their full length due to a failure of flame or shockpropagation along the cord. For reasons that have not been understoodprior to the present invention, these lower strength lines would explodeover only a short portion of their upper lengths. In other instanceseither the wire line was severed or serious damage caused to the casing,or both, for reasons not understood or readily explained. It has beendiscovered that, in most instances, these accidents are produced invarious ways including in particular stretching, ballooning and loopingof the cord due to a number of factors including axial shifting of thewire line centralizers or other anchorage securing the cord to the wireline, the adverse affect on the cord of the very substantial sub-surfaceambient temperatures customarily encountered at lower levels in oilwells and the high drag forces acting on the cord as it is loweredthrough the mud and other fluids customarily present in a well. As aresult of this stretching or the shifting of the cord anchorage thedistance between adjacent grains leads to propagation failure. It canalso result in excess portions of the stretched cord ballooninglaterally close to or against the casing and, under more extremeconditions, collecting in a loop adjacent an anchorage connectionbetween the cord and the wire line. Upon detonation of the balloon orloop, or both, an unusually powerful blast is produced in a localizedarea of the well which not infrequently cuts the wire line and releasesthe line weight but can cause serious damage to the casing itself.

it has been proposed heretofore to assemble a pair of explosive cords inparallel along the wire line and to explode them separately either byusing a single or separate pairs of electrical leads. If the same pairis used, then both cords are set off in fast unregulatable sequence. Theuse of separate lead wires for each explosive cord enables the operatorto vary the interval between detonations but is subject to the seriousdisadvantage of having to provide and protect separate leads for eachcharge. This complicates the equipment and servicing operation andinvolves the risk of severing one or more of the lead in wires andgreatly increases the risk of malfunctions as well as the maintenanceand handling costs.

Other problems associated with string shot operations as heretoforeconducted involve the problem of equipping the wire line with thecentralizer devices to hold the line out of contact with the casingsidewall and couplings during the runin and pullout cycle as well as tosafeguard the explosive cord against damage during the loweringoperation. These centralizers are required at frequent intervals alongthe wire line and their presence on the line interferes with reeling andstorage of the line.

The foregoing and other serious disadvantages accompanying string shotoperations as heretofore conducted are avoided by the present inventionusing the equipment and the improved techniques provided by thisinvention. A simple wire line is employed having a central conductor anda second conductor comprising the metallic sheath of the line which areutilized to supply the electrical energy required to detonate one or aseries of explosive cords in any desired time interval or simultaneouslyin one or more groups if so desired. Explosive cording incorporatingmeans safeguarding against stretch and malfunctioning of the cord andretarding temperature rise of the explosive itself makes possible theuse of lower explosive strength cord than heretofore possible andnumerous other advantages.

An improved centralizer construction permits the centralizer to beinstalled and removed from the wire line expeditiously at the well head.After the main body of the centralizer has been detached, the wire linecan be compactly reeled on the takeup spool or storage reel. As soon asthe centralizer is installed on the wire line one or more lengths ofexplosive cord can be secured to the periphery of its main bodyfollowing which the wire line is lowered into the well until in positionto receive the next centralizer.

The selective detonation of explosive cords via a single pair ofconductors is made possible by unique electrical discriminator meansconnected between one of the conductive paths and the detonators foreach cord. Typically the dis criminator utilizes semiconductors arrangedto pass electrical energy only to a particular cord or to a set of cordsselected for detonation at a particular time. Greater versatility isachieved by utilizing the discriminator in combination with a reversingswitch and means for controlling the applied potential.

Another feature of the invention is the provision of a blowout protectorof simple unique design across the wellhead. This protector includes acover having a nonconductive gasket which fits tightly about the wireline in the closed position of the protector and which opens for thefull diameter of the casing whenever the wire line is being lowered orwithdrawn.

Accordingly, it is an object of the present invention to provide aunique, improved method for conducting string shot operations in a wellin such manner as to safeguard against ballooning and looping of theexplosive cord during lowering of the same into a well.

Another object of the invention is the provision of a method forlowering multiple string shots simultaneously into a well in a mannersafeguarding against ballooning and looping of the several string shotsand for separately detonating said string shots at will during a singlewire line run-in operation.

Another object of the invention is the provision of a method utilizing atwo-conductor wire line to detonate one or more string shotssimultaneously or in any desired order and time intervals.

These and other more specific objects will appear upon reading thefollowing specification and claims and upon considering in connectiontherewith the attached drawing to which they relate.

Referring now to the drawing in which a preferred embodiment of theinvention is illustrated:

FIG. 1 is a vertical sectional view of a well having a perforated casingand showing an illustrative embodiment of the invention string shotapparatus in position for detonation of its separate cords;

FIG. 2 is a top plan view on an enlarged scale of the blowout protectorclosed against the wellhead;

FIG. 3 is a cross-sectional view taken along line 3-3 on FIG. 2;

.FIG. 4 is a cross-sectional view taken along line 4-4 on FIG. 3;

FIG. 5 is a diagrammatic elevational view at the wellhead showingdetails of the means for installing the explosive along the wire line ata desired uniform tension;

FIG. 6 is a schematic view of an illustrative embodiment of theelectrical firing circuit for a plurality of explosive cords;

FIG, 7 is an elevational view on an enlarged scale of means for securingthe explosive cords to an adjacent portion of the wire line;

FIG. 8 is a cross-sectional view taken along line 88 on FIG. "'2

FIG. 9 is a fragmentary enlarged view of the explosive cord;

.FIG. 10 is an elevational view of one preferred embodiment of the wireline centralizer.

FIG. 11 is a top plan view taken on FIG. 10;

FIG. 12 is a cross-sectional view taken along line 12-12 on FIG. 10: and

FIG. 13 is an elevational view of a second preferred form of ihecentralizer assembled to the wire line.

lReferring initially and more particularly to FIG. 1, there is shown anoil well casing 10 having a multiplicity of flow perforations lldistributed along its sidewall at the production llow level. It will beunderstood that these perforations may be distributed over many feet ofthe casing and in one or more areas of the casing. Secured to the top ofthe casing IS a radial lllange 12 to which a blowout protector mountingring 13 is detachably secured, as by bolts 15. This ring has a centralopening 16. corresponding to the ID. of the casing so as not to restrictthe entrance to the well. Opening 16 is provided with a cover 17 hereshown as formed in a single part and equipped with a hinge 18 secured tomounting ring 13. However. it will be understood that cover 17 may beformed in two halves each having its own hinge connection with mountingring 13 if so desired. Threaded studs 20 welded or otherwise secured tomounting ring 13 pass through openings in cover 17 and support thumbnuts 22 for clamping the cover firmly sealed closed prior to a stringshot firing operation.

Suitably secured to cover 17 and mounting ring 13 is a twopart or splitsealing gasket 23.24 having its edge portions iiihaped to clamp snuglyabout the wire line 25 when cover 17 is closed. Each of the gaskethalves 23.24 are suitably and firmly anchored to the cover and to themounting ring as in the manner indicated in FIGS. 2 and 4. Thesenonconductive sealing gaskets not only provide a l'luidtight seal aboutthe wire line but isolate the line and its conductors electrically fromthe casing.

Wire line 25 includes a central conductor 26 separated from the helicalsheath conductors 27 which also serve as the iiecond conductive pathemployed as will be explained presently to provide one portion of theelectrical circuit between the direct current power source 28 (FIG. 6)and one or more string shots. Typically wire line 25 passes over a guidepulley 30 overlying the well and thence to a storage reel, not shown,but of any suitable well-known construction driven by reversible powermeans for handling the wire line.

Referring now more particularly to FIGS. 1, I0. 11 and 12, it will beunderstood that wire line 25 includes a weight at its lower end ofadequate size to facilitate the expeditious lowering of the wire lineinto the well through the thick fluids generally present in the well.Distributed along the lower portion of the wire line at suitableintervals. as 10 to 25 feet, are a plurality of centralizers 40,40. Asis best shown in FIGS. 10 to 12, each centralizer includes a mandrel 41having a diameter similar to that of wire line 25 and provided at itsopposite ends with enlargements such as yokes 42. These yokes are formedwith aligned openings 43 each equipped with a pivot pin 44 suitablysecured in place and extending through a loop 45 of the wire line or ofa similar cable 46 interconnecting adjacent ones of the centralizermandrels.

lLoosely fitting over the midportions of mandrels 41 is the main body 48of the centralizer. This main body is generally cylindrical in contourand has a long deep slot 49 opening through one sidewall and sized tofit readily over mandrel 41.

Main body 48 is slightly shorter than the distance between the adjacentends of yokes 42, and is formed with a threaded bore seating a thumbscrew 50 having a knurled head. Its inner end extends into slot 49 inposition to engage the mandrel and hold the centralizer body firmlylocked in assembled position in the manner made clear by FIG. 12.

Extending crosswise of the opposite ends of the centralizer bodies 48are pairs of passages 51 loosely seating highly tempered wire loops 53.As herein shown, each centralizer is proided with a single pair of thesewire loops shaped as best ihown in FIG. 10 and each including oppositelydirected iemicylindrical loops projecting radially from the sidewall ofmain body 48. Since each of these loops lies at an angle to the portionslocated in passages 51, the loops are held against sliding movementlengthwise of these passages. The radial extent of each of the loops issuch that they cooperate in holding the wire line loosely centralized inthe well casing.

A second and simpler embodiment of the invention centralizer 40',illustrated in FIG. 13, may be mounted directly on wire line 25 at anysuitable spacing therealong. For this purpose the wire line is providedwith enlargements, such as collars 60, telescoped over one end of thewire line and then subiected to high-pressure contraction forcesadequate to squeeze the ductile collar material into interlockinggripping action with the wire sheath of the wire line. It will also beunderstood that the collars may be brazed or otherwise firmly secured tothe wire line. These collars pass readily over the storage reel for thewire line.

The main body 48 of the centralizer is formed with slot 49 similar tothe corresponding slot in FIGS. 10 and 12 and sized to fit readily overthe wire line. Intermediate the opposite ends of this slot there IS anenlarged U-shaped recess 61 shaped to [It loosely about and accommodatecollar 60 in the manner made clear by FIG. 13. A thumb screw 50' iscarried in main body 48 and serves similarly to the corresponding thumbscrew in FIGS. 10 to 12 to hold the centralizer assembled to 'he wireline. Additionally main body 48' is equipped with Wire loops 53' in thesame manner described above in connection with FIGS. 10 to 12. It istherefore evident that the thumb screw 50' holds the centralizerdetachably assembled to the wire line whereas collar 60 cooperates withrecess 61 to hold the centralizer against movement longitudinally of thewire line. The simplified centralizer avoids the need for theyokeequipped mandrels as well as for separate lengths of cabling 46interconnecting adjacent centralizers.

The assembly of the explosive cord through the wire line will now bedescribed with the aid of FIGS. 1 and 5. The crew attaches weight 35 tothe lowermost end of the wire line and inserts this weight into the topof the well. As shown in FIGS. 1 and 5, only a pair of explosive cords65,66 are shown. In many operations a single pair suffices but in otherit may be desirable to fit the wire line with a larger number of stringshots. In this case, it is usually preferable to use explosive cord ofconsiderably smaller size and explosive power than that heretot'oreemployed. For example, it has been common practice heretofore not to useexplosive cord smaller than 25 grain size in string shot operations.However, by this invention, it is feasible and advantageous to use cordof the smallest commercial size, namely 4 grain as well as various sizesintermediate 4 grain and 2S grain provided adequate precautions aretaken against elongation of the cord while being lowered into the well.Such precautions may comprise firm anchorage of the cord to the wireline at closely spaced intervals and/or the use of cord in accordancewith the present invention incorporating builtin stretch resisting meanssuch as nonstretching small wires or other high-strength nonstretchingfilaments 68,68. These may take the place of a corresponding number offilaments of the outer protective sheath of the cord in the manner shownin FIG. 9. As there shown, the nonstretching filaments 68 are wrappedspirally in opposite directions between ad- ,iacent spiral wrappings69.69 of the conventional cord sheath. It will be understood that theexplosive cord is otherwise of any suitable conventional designincluding a central core of explosive material 70 encased within a toughflexible tubular shroud 71 of plastic or the like. The latter isembraced by the wax-covered braided sheath 69,69.

Desirably, the explosive core 65,66 is assembled lengthwise of the wireline in a taut condition and preloaded to a suitable uniform tension.According to this invention, this is accomplished in the mannerillustrated in FIG. 5 and showing the tensioning equipment for one onlyof the cords, it being understood that cord 66 passes over similarautomatic tensioning equipment. The cord passes from a supply reel 73mounted on a suitable support 74, and thence over an idler pulley 75.The cord is held firmly seated on pulley 75 by a pivotally supportedidler pulley 76 and a tension spring 77. The cord then passes over apair ofidlers 78 between which there is mounted a pulley 79 on which anysuitable member of removable tensionregulating weights 80,80 can bemounted. The cord then passes over an idler 82 carried by the hanger 83for wire line guide pulley 30, pulley 82 being appropriately positionedclose to one side of the wire line at the point of entry into the wellhead.

It will be understood that the wire line leaves the powerdriven wireline reel carrying only mandrels 41 or their equivalent such as collars60 (FIG. 13). As these components approach entry into the well head, thewire line is stopped while the crew inserts the main body 48 or 48 ofthe centralizer and secures it in place by tightening thumb nut 50 or50'. At the same time the explosive cords are securely anchored to themain body of the centralizer by serving the same tapes or tie-bands 85(FIG. 1). The crew then proceeds to lower the wire line along with theattached explosive cords under appropriate tension as determined by theweights 80 carried by the pulley 79. Centralizers continue to beassembled to the wire line in succession and anchored to the explosivecords as described.

If the centralizers are spaced considerable distances apart or in caseswhere smaller size explosive cord is being used, it is desirable toanchor the cords to the wire line at one or more points between adjacentcentralizers. This is done using cylinders 90 constructed as shown inFIGS. 7 and 8. These anchor members are secured to the wire line byswaging, brazing or other suitable means. Each member 90 is formed withlong grooves 91 of V-shape in cross section extending lengthwise of thebody and sized to grip cords 65,66 firmly irrespective of the particularsize being used. A deep annular groove encircling the midportion ofmember 90 accommodates tape or banding 93 applied over the cords 65,66to clamp the latter firmly within grooves 91.

The equipment employed in connection with the two conductors 26,27 ofthe wire line to detonate the explosive cords according to one preferredembodiment is illustrated schematically in FIG. 6. The upper ends ofconductors 26,27 are connected to battery 28 by way of a double-throwreversing switch 95 and a rheostat 96. The lower end of the wire lineclosest to the upper end of the explosive cords is connected to the cordby way of an electrical discriminator 97. This discriminator preferablycomprises a thick-walled tubular housing 98 of nonconductive materialcharged with potting compound encapsulating at least one and preferablyseveral semiconductors 99a, 99b, connected in series parallel with oneof the wire line conductors as conductor 27. The other conductor 26 isconnected to a common bus 100 connected in turn to one terminal of eachof the cord detonators 101. The other lead 102 of each detonator isconnected to a terminal post 103 in the sidewall of discriminator 98 andconnected as shown in FIG. 6 to a respective one of the semiconductors99a,99b.

The detonators 101 are preferably arranged in vertically staggeredrelation as indicated in FIGS. 1 and 6 and are sufficiently spaced fromone another that the detonation of one does not cause detonation Manyother detonator, or the premature ignition of any explosive cord.

In some service operations only two or three explosive cords are securedto the wire line during single run in operations. In

this case, ordinary diodes may be used. However when employing a largernumber of string shots, such as is indicated in FIG. 6 at 65, 66', 65",66", 65", then it is desirable to employ Zener-type diodes 99a,99b of anappropriate voltage rating to be triggered by a particular voltageapplied thereto by adjusting the contactor of rheostat 96. It will benoted that diodes 99a are connected in series to pass current of aparticular polarity whereas diodes 99b are connected in series with oneanother in a parallel circuit and are triggered to pass current only byvoltage of an opposite polarity.

The operation of the equipment will now be described, it being assumedthat perforations 11 of well casing 10 are plugged with sand or otherdebris interfering with the well flow. To remove this debris and restorefull flow conditions, the service crew connects the blowout preventorassembly to the top of the well casing using assembly bolts 15 and thenproceed to lower weight 35 of the wire line toward the wellhead. As thisweight is about to disappear into the casing the main body assembly 48of the first centralizer is inserted crosswise of the wire line andlocked in place by tightening thumb screw 51. The selected number ofstring shot cords are then threaded through the tension controlequipment shown in FIG. 5 and their free ends are firmly secured to theopposite sides of the first centralizer by banding 85. The wire line isthen lowered into the well and successive ones of the centralizer bodiesare assembled to the line and taped in place. If the intermediate cordanchorages 90, such as those shown in FIGS. 6 and 7 are employed, theexplosive cords are inserted into the V-shaped slots 91 of theseanchorages and taped firmly in place.

After all of the centralizers have been installed and the tensionedexplosive cords have been secured to the sides of the wire line in themannerjust described, their upper ends are cut off in echelon and eachis provided with a detonator cap 101 and connected in circuit with arespective terminal 103 of discriminator 97. The lead wires to thediscriminator and to the detonator bus 100 are also completed followingwhich the wire line is lowered into the well until the string shots arelocated directly opposite the perforations to be cleared of debris.Cover 17 of the blowout preventor is then closed and locked in place bythumb nuts 22 to avoid any possibility that the string shot operationswill open a high-pressure area of the earth formation into the well andinitiate high-pressure flow from the top of the well.

Before closing switch 95, the operator makes certain that rheostatregulator 96 is adjusted to its upper end or a harmless positionineffective to activate any detonator. The switch is then closed and thefirst cord is fired by adjusting rheostat 96 downwardly until thevoltage increases sufficiently to fire the first string shot 65. No oneof the other string shots 66,66 or 66" will fire because the voltage isinadequate to trigger any one of the Zener diodes 99a. The second stringshot 66 will be detonated simply by shifting the rheostat in a directionto increase the applied voltage to a value triggering the upper one ofdiodes 990. In this same manner the operator can proceed to detonatecords 66 and 66" in any desired time interval by regulation of rheostat96.

He may then proceed to detonate the remainder of the cords by returningthe rheostat to its initial position and close switch in the oppositedirection thereby reversing the polarity of the applied voltage. Theoperator then proceeds to adjust the voltage in steps as before tovalues adequate to fire cords 65', 65", 65".

Should the operator desire to fire more than one cord simultaneously, headjusts the voltage regulator 96 to the appropriate voltage known asrequired to assure triggering the desired number of diodes and thencloses the switch in the proper direction to trigger these selecteddiodes.

It will therefore be apparent from the foregoing that a highly versatiletechnique has been provided for performing string shot serviceoperations on oil wells having faulty flow characteristics. Thetechnique makes it possible to employ any desired number of string shotsusing the smallest available grain rating and including a series oflarger grain rating and to explode these in succession or in any desiredgroupings until full flow conditions are restored. The technique permitswell flow tests to be conducted between individual detonations todetermine the effectiveness thereof. following which additionalexplosions of any selected size and number may be performed or. if testsshow that full flow has been restored. the servicing operation can beimmediately discontinued and the wire line withdrawn from the well.

The withdrawal operation is performed after opening cover l7 and thenreeling in the line until the discriminator 97 and the centralizer exitfrom the well head. These are removed as are successive othercentralizers in a simple and expeditious manner until the withdrawaloperation has been completed.

While the particular method of conducting string shot operations hereinshown and disclosed in detail is fully capalble of attaining the objectsand providing the advantages ihereinbefore stated, it is to beunderstood that it is merely illustrative of the presently preferredembodiments of the invention. and that no limitations are intended tothe details of construction or design herein shown other than as definedin the appended claims.

l claim:

ll. That method of servicing an oil well with an explosive charge toremove debris from the oil inlet performations distributed along thesidewall thereof which comprises: lowering into the mouth of the well aweighted flexible wire line equipped with a pair of electricalconductors and a multiplicity of spaced apart enlargements fixedthereto, attaching quickly attachable and detachable centralizers tosaid wire line from the side thereof immediately adjacent first one andthen another of said enlargements as said wire line is lowered lll'llOthe well and held positively against axial movement along the wire lineby said enlargements and effective to hold the wire line spacedgenerally centrally of the well. attaching an elongated explosive cordalong centralizer-equipped portions of said wire line and close to theside of the wire line so as to restrain said explosive cord againstelongation and ballooning by frictional drag forces as it is loweredthru well fluid of increasing temperature. connecting one end of saidexplosive cord to electrical detonator means connected in circuit withsaid electrical conductors. and closing a power circuit through saidpair of conductors and said detonator means to detonate said explosivecord after it is positioned opposite said distributed oil inletperforations.

12. That method defined in claim 1 characterized in the steps ofattaching an explosive cord to said wire line having builtin stretchrestraining means. and connecting said explosive cord to the wire lineat intervals therealong spaced sufficiently close together to hold saidexplosive cord generally centered along the well.

.3. That method defined in claim 1 characterized in the steps ofrestraining said explosive cord against stretching while being loweredinto the well by securing the same to said wire line in such manner asto utilize the strength of the wire line to prevent stretching of theexplosive cord.

l. That method defined in claim 1 characterized in the step of closingthe mouth of the well in a fluidtight manner about a contiguous portionof the wire line after the line has been lowered to a desired level inthe well and before detonating said explosive cord.

5. That method defined in claim 1 characterized in the step of attachinga centralizer to the wire line from one side thereof immediatelyadjacent a selected one of said stop means before the latter passes intothe mouth of the well.

6. That method defined in claim 5 characterized in the step ofwithdrawing said wire line after said explosive cord has been detonatedand coiling the line and said spaced-apart enllargements on power-drivenstorage reel means. and detaching said centralizers in succession as thesame emerge from the well mouth and before the emerging centralizerteaches said storage reel means.

T. in a method of performing a servicing operation in a deep earth boresubject to high earth bore temperature by detonating an elongatedexplosive cord along the length of the bore, said method comprising thesteps of securing to the side of a weighted flexible wire line means anelongated explosive cord incorporating builtin antistretching means tocounteract deep earth bore temperature conditions and friction and dragforces acting thereon as said explosive cord is lowered through fluidpresent in the bore. applying and immovably anchoring individualcentralizers to said wire line means from the side thereof at spacedintervals therealong and between the opposite ends of said explosivecord as successive lengths of said wire line approach the entrance tothe earth bore to hold said wire line means and said explosive cordgenerally centrally of the earth bore providing said explosive cordmeans with detonator means, and activating said detonator means todetonate said explosive cord means after the latter has been adjusted toa desired zone lengthwise of the earth bore. withdrawing said wire linemeans from the earth bore onto reeling means for said wire line means,and detaching each of said centralizers from said wire line means assuccessive ones thereof emerge from the entrance to the earth bore.

3. That method defined in claim 7 characterized in the steps ofequipping said wire line means at spaced-apart intervals along thelength thereof with quickly attachable and detachable centralizer meansfor holding at least those portions of said wire line means contiguousto said explosive cord out of contact with the sides of said earth bore.

9. That method defined in claim 7 characterized in the steps of securingspaced-apart portions of said explosive cord to juxtaposed portions ofsaid wire line means.

10. That method defined in claim 7 characterized in the step of wrappingspaced-apart lengths of said wire line means and said explosive cordwith tie means to hold said explosive cord in assembled positiontherealong and substantially fully exposed from all sides thereof as thesame is lowered into an earth bore or the like.

ll. That method defined in claim 8 characterized in the steps of storingsaid flexible wire line means on power-driven storage reel means.introducing the weighted free end of said wire line means into an earthbore to be serviced. attaching individual ones of said centralizer meansto said wire line means at intervals therealong, and securing saidexplosive cord means to the exterior of said wire line means atsuccessive intervals spaced therealong and as additional portions ofsaid wire line means are lowered into the upper end of the earth bore.

.12. That method defined in claim 11 characterized in the stepsofwithdrawing said wire line means after detonating said cord means andstoring the line means on said storage reel means while detachingsuccessive ones of said centralizer means as the same emerge from theearth bore thereby to facilitate reeling the line means and the compactstowage thereof while moving to the next earth bore in need of a serviceoperation.

13. That method defined in claim 7 characterized in the steps ofsecuring a plurality of the same type of said explosive cord means inparallel with one another lengthwise of said wire line means. andproviding explosive cord with separate detonator means. and connectingsaid detonator means in cirsuit with electrical signal discriminatormeans selectively responsive to electrical energy of differentdistinctive characteristics to detonate said explosive cord meansindividually and at the option of control means at the upper end of saidearth bore.

14. That method defined in claim 7 characterized in the step of securingsaid explosive cord means to said suspension line means while said cordmeans is held taut under tension of a selected value adequate to assurethe absence of slackness therealong during said securing operation.

l5. That method defined in claim 7 characterized in the step of securingsaid explosive cord means to said wire line means without slack incontiguous lengths of said cord means and said wire line means.

16. In a method of performing a servicing operation in a well casing bydetonating explosive cords supported along the side of a wire line andlocated centrally of and opposite a sidewall of the well casing to beserviced, that improvement which comprises: the steps of supporting aplurality of explosive cords parallel to one another along the wire linein a manner to prevent harmful ballooning and looping thereof as saidcords are subjected to temperature rise and drag forces as the same arelowered into a well casing, providing each explosive cord with separatedetonator means in circuit with means selectively responsive toelectrical energy of different distinctive characteristics to detonate aselected one only of said explosive cords as electrical energy havingone of said different distinctive characteristics is applied thereto,and applying electrical energy having the appropriate respectivedistinctive characteristics to said detonator means to detonate saidexplosive cords in sequence in any desired time-delayed pattern.

17. That method defined in claim 16 characterized in the step ofutilizing detonator means in circuit with means selectively responsiveto energization by electrical energy of different polarity, andenergizing said detonator means in timed sequence with electrical energyof different polarity.

18. That method defined in claim 16 characterized in the step ofutilizing detonator means in circuit with means selectively responsiveto energization by voltages of different potential levels, and applyingelectrical energy to said detonator means in time-delayed sequence atsaid different potential levels thereby to detonate said explosive cordsin time-delayed sequence.

19. That method defined in claim 16 characterized in the step ofutilizing solid-state devices connected in circuit between saidexplosive cords and a pair of conductors forming part of said wire line.

20. That method defined in claim 16 characterized in the step of sealingthe upper end of the well casing while said explosive cords are beingdetonated to safeguard against the expulsion of well fluid if one ormore of the detonations release subsurface pressures into the well.

21. That method defined in claim 20 characterized in the steps ofproviding the lower end ofsaid wire line with a plurality ofcentralizers spaced lengthwise therealong, suspending said explosivecords alongside said wire line between successive ones of saidcentralizers, and securing said explosive cords to spaced points aboutthe periphery of said centralizers to isolate the drag forces acting onthe explosive cords to either vertical side of the centralizers whilebeing lowered through the well fluid.

22. That method defined in claim 16 characterized in the step ofproviding a single pair of conductors extending lengthwise of said wireline, connecting all of said detonator means in circuit with the lowerend of said pair of conductors, and applying electrical energy of firstone and then another of said different electrical characteristics to theupper ends of said pair of conductors.

23. That method defined in claim 16 characterized in the step ofsecuring said explosive cords to spaced points along the length of saidwire line while said explosive cords are loaded in tension to apredetermined load.

24. That method defined in claim 16 characterized in the step ofsecuring said explosive cord to said wire line while held taut therebyto safeguard against objectionable elongation of said explosive cord andthe possibility of a loop forming in said cord due to the elongationthereby while being lowered into the well.

25. In a method of performing a servicing operation in a deep floodedwell casing to reopen the inlet perforations by detonating explosivecord means supported lengthwise of the interior of the well casing overa length coextensive with the length of the perforated inlet sectionthereof, that improvement which comprises the steps of lowering tautflexible wire line means into a flooded well casing along with many rodsof exposed explosive cord means secured along the side of said wire linemeans at spaced intervals and generally parallel thereto and anchoredagainst looping, ballooning, tensionin and stretching effective to causema unctionmg of 831d cor means or damage to the well casing when saidcord means is detonated and which looping, ballooning and stretching iscaused by temperature rises and by drag forces acting on said explosivecord means while lowering the same into said deep flooded well casing.

1. That method of servicing an oil well with an explosive charge toremove debris from the oil inlet performations distributed along thesidewall thereof which comprises: lowering into the mouth of the well aweighted flexible wire line equipped with a pair of electricalconductors and a multiplicity of spaced apart enlargements fixedthereto, attaching quickly attachable and detachable centralizers tosaid wire line from the side thereof immediately adjacent first one andthen another of said enlargements as said wire line is lowered into thewell and held positively against axial movement along the wire line bysaid enlargements and effective to hold the wire line spaced generallycentrally of the well, attaching an elongated explosive cord alongcentralizer-equipped portions of said wire line and close to the side ofthe wire line so as to restrain said explosive cord against elongationand ballooning by frictional drag forces as it is lowered thru wellfluid of increasing temperature, connecting one end of said explosivecord to electrical detonator means connected in circuit with saidelectrical conductors, and closing a power circuit through said pair ofconductors and said detonator means to detonate said explosive cordafter it is positioned opposite said distributed oil inlet perforations.2. That method defined in claim 1 characterized in the steps ofattaching an explosive cord to said wire line having builtin stretchrestraining means, and connecting said explosive cord to the wire lineat intervals therealong spaced sufficiently close together to hold saidexplosive cord generally centered along the well.
 3. That method definedin claim 1 characterized in the steps of restraining said explosive cordagainst stretching while being lowered into the well by securing thesame to said wire line in such manner as to utilize the strength of thewire line to prevent stretching of the explosive cord.
 4. That methoddefined in claim 1 characterized in the step of closing the mouth of thewell in a fluidtight manner about a contiguous portion of the wire lineafter the line has been lowered to a desired level in the well andbefore detonating said explosive cord.
 5. That method defined in claim 1characterized in the step of attaching a centralizer to the wire linefrom one side thereof immediately adjacent a selected one of said stopmeans before the latter passes into the mouth of the well.
 6. Thatmethod defined in claim 5 characterized in the step of withdrawing saidwire line after said explosive cord has been detonated and coiling theline and said spaced-apart enlargements on power-driven storage reelmeans, and detaching said centralizers in succession as the same emergefrom the well mouth and before the emerging centralizer reaches saidstorage reel means.
 7. In a method of performing a servicing operationin a deep earth bore subject to high earth bore temperature bydetonating an elongated explosive cord along the length of the bore,said method comprising the steps of securing to the side of a weightedflexible wire line means an elongated explosive cord incorporatingbuiltin antistretching means to counteract deep earth bore temperatureconditions and friction and drag forces acting thereon as said explosivecord is lowered through fluid present in the bore, applying andimmovabLy anchoring individual centralizers to said wire line means fromthe side thereof at spaced intervals therealong and between the oppositeends of said explosive cord as successive lengths of said wire lineapproach the entrance to the earth bore to hold said wire line means andsaid explosive cord generally centrally of the earth bore providing saidexplosive cord means with detonator means, and activating said detonatormeans to detonate said explosive cord means after the latter has beenadjusted to a desired zone lengthwise of the earth bore, withdrawingsaid wire line means from the earth bore onto reeling means for saidwire line means, and detaching each of said centralizers from said wireline means as successive ones thereof emerge from the entrance to theearth bore.
 8. That method defined in claim 7 characterized in the stepsof equipping said wire line means at spaced-apart intervals along thelength thereof with quickly attachable and detachable centralizer meansfor holding at least those portions of said wire line means contiguousto said explosive cord out of contact with the sides of said earth bore.9. That method defined in claim 7 characterized in the steps of securingspaced-apart portions of said explosive cord to juxtaposed portions ofsaid wire line means.
 10. That method defined in claim 7 characterizedin the step of wrapping spaced-apart lengths of said wire line means andsaid explosive cord with tie means to hold said explosive cord inassembled position therealong and substantially fully exposed from allsides thereof as the same is lowered into an earth bore or the like. 11.That method defined in claim 8 characterized in the steps of storingsaid flexible wire line means on power-driven storage reel means,introducing the weighted free end of said wire line means into an earthbore to be serviced, attaching individual ones of said centralizer meansto said wire line means at intervals therealong, and securing saidexplosive cord means to the exterior of said wire line means atsuccessive intervals spaced therealong and as additional portions ofsaid wire line means are lowered into the upper end of the earth bore.12. That method defined in claim 11 characterized in the steps ofwithdrawing said wire line means after detonating said cord means andstoring the line means on said storage reel means while detachingsuccessive ones of said centralizer means as the same emerge from theearth bore thereby to facilitate reeling the line means and the compactstowage thereof while moving to the next earth bore in need of a serviceoperation.
 13. That method defined in claim 7 characterized in the stepsof securing a plurality of the same type of said explosive cord means inparallel with one another lengthwise of said wire line means, andproviding explosive cord with separate detonator means, and connectingsaid detonator means in circuit with electrical signal discriminatormeans selectively responsive to electrical energy of differentdistinctive characteristics to detonate said explosive cord meansindividually and at the option of control means at the upper end of saidearth bore.
 14. That method defined in claim 7 characterized in the stepof securing said explosive cord means to said suspension line meanswhile said cord means is held taut under tension of a selected valueadequate to assure the absence of slackness therealong during saidsecuring operation.
 15. That method defined in claim 7 characterized inthe step of securing said explosive cord means to said wire line meanswithout slack in contiguous lengths of said cord means and said wireline means.
 16. In a method of performing a servicing operation in awell casing by detonating explosive cords supported along the side of awire line and located centrally of and opposite a sidewall of the wellcasing to be serviced, that improvement which comprises: the steps ofsupporting a plurality of explosive cords parallel to one another alongthe wire lIne in a manner to prevent harmful ballooning and loopingthereof as said cords are subjected to temperature rise and drag forcesas the same are lowered into a well casing, providing each explosivecord with separate detonator means in circuit with means selectivelyresponsive to electrical energy of different distinctive characteristicsto detonate a selected one only of said explosive cords as electricalenergy having one of said different distinctive characteristics isapplied thereto, and applying electrical energy having the appropriaterespective distinctive characteristics to said detonator means todetonate said explosive cords in sequence in any desired time-delayedpattern.
 17. That method defined in claim 16 characterized in the stepof utilizing detonator means in circuit with means selectivelyresponsive to energization by electrical energy of different polarity,and energizing said detonator means in timed sequence with electricalenergy of different polarity.
 18. That method defined in claim 16characterized in the step of utilizing detonator means in circuit withmeans selectively responsive to energization by voltages of differentpotential levels, and applying electrical energy to said detonator meansin time-delayed sequence at said different potential levels thereby todetonate said explosive cords in time-delayed sequence.
 19. That methoddefined in claim 16 characterized in the step of utilizing solid-statedevices connected in circuit between said explosive cords and a pair ofconductors forming part of said wire line.
 20. That method defined inclaim 16 characterized in the step of sealing the upper end of the wellcasing while said explosive cords are being detonated to safeguardagainst the expulsion of well fluid if one or more of the detonationsrelease subsurface pressures into the well.
 21. That method defined inclaim 20 characterized in the steps of providing the lower end of saidwire line with a plurality of centralizers spaced lengthwise therealong,suspending said explosive cords alongside said wire line betweensuccessive ones of said centralizers, and securing said explosive cordsto spaced points about the periphery of said centralizers to isolate thedrag forces acting on the explosive cords to either vertical side of thecentralizers while being lowered through the well fluid.
 22. That methoddefined in claim 16 characterized in the step of providing a single pairof conductors extending lengthwise of said wire line, connecting all ofsaid detonator means in circuit with the lower end of said pair ofconductors, and applying electrical energy of first one and then anotherof said different electrical characteristics to the upper ends of saidpair of conductors.
 23. That method defined in claim 16 characterized inthe step of securing said explosive cords to spaced points along thelength of said wire line while said explosive cords are loaded intension to a predetermined load.
 24. That method defined in claim 16characterized in the step of securing said explosive cord to said wireline while held taut thereby to safeguard against objectionableelongation of said explosive cord and the possibility of a loop formingin said cord due to the elongation thereby while being lowered into thewell.
 25. In a method of performing a servicing operation in a deepflooded well casing to reopen the inlet perforations by detonatingexplosive cord means supported lengthwise of the interior of the wellcasing over a length coextensive with the length of the perforated inletsection thereof, that improvement which comprises the steps of loweringtaut flexible wire line means into a flooded well casing along with manyrods of exposed explosive cord means secured along the side of said wireline means at spaced intervals and generally parallel thereto andanchored against looping, ballooning, tensioning and stretchingeffective to cause malfunctioning of said cord means or damage to thewell casing when said cord meanS is detonated and which looping,ballooning and stretching is caused by temperature rises and by dragforces acting on said explosive cord means while lowering the same intosaid deep flooded well casing.